1. Field of the Invention
Apparatuses consistent with the present invention relate to an electromagnetic micro-actuator, and more particularly, to an electromagnetic micro-actuator having an improved driving coil that drives a stage on which a mirror face is formed.
2. Description of the Related Art
Recently, researches about electromagnetic micro-actuators manufactured using micro-machining techniques have been actively conducted in various technical fields such as displays, laser printers, precise measurement devices, and precise processing. For example, the electromagnetic micro-actuators can be used in an optical scanner for reflecting scanning light towards an image region in a screen.
The optical scanner includes a mirror surface to reflect incident light, and the mirror surface vibrates with respect to vibration axes that are different from each other to scan incident light emitted from a light source on an image region in vertical or horizontal directions. Light beams reflected by the mirror surface form a plurality of scanning lines on the image region by oscillating in a given scanning angle in the horizontal direction, and the scanning angle variations in the horizontal direction can be a sine wave that reciprocally vibrates with a high frequency. When a scanning of an image has been completed by moving a beam spot from an upper end position to a lower end position of the image, the scanning beam oscillates within a predetermined scanning angle in the vertical direction in order to relocate the beam spot to the upper end position of the image. The vertical scanning signal may be expressed as a function of a saw-tooth type wave.
An electromagnetic actuator that uses a magnetic apparatus, for example, an electromagnet or a permanent magnet, horizontally and vertically scans a mirror unit by applying a magnetic field to a driving coil that surrounds the mirror unit.
However, when a signal that is used for horizontal scanning and another signal that is used for vertical scanning are simultaneously applied to one driving coil, the horizontal scanning signal and the vertical scanning signal overlap, and thus, a maximum current increases, thereby resulting in an increase of power consumption.
However, when a horizontal scanning coil and a vertical scanning coil are formed on an inner frame that supports the mirror unit and on an external frame that supports the inner frame, respectively, the horizontal scanning coil has a reduced distance from the mirror unit, thereby reducing the rotational moment. The reduced rotational moment reduces a driving angle and may cause thermal deformation of a portion of the horizontal scanning coil by forming the high frequency horizontal scanning coil in a small area.
In order to scan an image on a screen located at the outside using an optical scanner, a scanning line can be scanned on the screen by vibrating the mirror, for example, in a saw-tooth type wave with a frequency of 60 Hz with respect to a horizontal torsion axis and in a sine wave with a relatively high frequency of approximately 20 KHz with respect to the vertical torsion axis. That is, the high frequency vibration in the vertical torsion axis horizontally scans the scanning line onto the screen, and the low frequency vibration in the horizontal torsion axis vertically scans the scanning line onto the screen, thereby realizing a two dimensional image on the screen.
In case of a resonance frequency of a mass that can vibrate with respect to the horizontal torsion axis of the mirror is designed to approximately 1 kHz, and a resonance frequency of a mass that can vibrate with respect to the vertical torsion axis is designed to approximately 20 kHz, when a 60 Hz saw-tooth type wave current and a modulated horizontal resonance frequency of 20 kHz are applied to the coil of the inner frame, a moment is generated in a direction vertical to the direction of a magnetic field applied from the outside. Such moment is used to drive the mirror by separating the moment into the horizontal torsion axis and the vertical torsion axis. Since the mirror resonates at a frequency of approximately 20 kHz with respect to the vertical torsion axis due to the synthesized moment, the mirror does not react to the 60 Hz saw-tooth type wave frequency component, however, is driven at a saw-tooth type wave frequency of 60 Hz with respect to the horizontal torsion axis.
However, the moment that acts on the horizontal torsion axis includes not only the 60 Hz saw-tooth type wave frequency component, but also includes the 20 kHz sine wave frequency component. Therefore, a minute vibration at the 20 kHz frequency occurs when the image is vertically scanned. That is, the horizontal torsion axis and the vertical torsion axis must independently vibrate by the low frequency signal (60 Hz) and the high frequency signal (20 kHz), respectively. However, the high frequency signal affects the vibration of the horizontal torsion axis that vibrates by the low frequency signal, thereby causing a minute vibration that prevents the scanning line from scanning on a desired point, and reducing resolution of an image. Hence, due to the vibration by the high frequency signal when a vertical scanning is performed, the horizontal scanning lines overlap each other. As a result, a high resolution image cannot be realized.
The vibration due to the high frequency signal is not only a problem to the scanner, but also to the entire electromagnetic actuator that requires a precise location control. In order to solve this problem, a circuitry configured with a low frequency pass filter can be employed. However, in this case, additional electronic parts are needed, and manufacturing costs increase.